Semipermeable membranes may be used for a wide variety of separations involving liquid-liquid separations, liquid-liquid solid separations and gas-gas separations. The membranes which are employed for these purposes usually comprise various organic polymers or mixtures of organic polymers either alone or supported on a porous backing material. For example, semipermeable membranes which are used in desalination processes can comprise cellulose acetate polymers composited on a porous support which acts as a backing for the membrane, thin film composite membranes comprising polymeric compounds such as polyethyleneimine, epiamine, polyethylene, polypropylene films also composited on a porous support such as a polysulfone member, etc. Likewise, gaseous separation membranes may comprise polymeric membranes of cellulose nitrate or cellulose acetate support membranes having a polymer such as dimethylsilicone, styrene, silicon-carbide copolymers composited thereon, as will as thin film membranes such as polymethylpentene polymers. In addition to these membranes other permselective membranes such as heteropoly acids may be employed for separating gases such as hydrogen from mixtures of gases in a gaseous stream.
In a majority of cases, the admixture of an organic compound, especially in a polymeric state, with an inorganic compound, results in a phase separation due to the fact that the two systems are immiscible in nature. However, we have now discovered that a thin film polymer blend membrane may be fabricated by admixing an inorganic compound of the type hereinafter set forth in greater detail with a combination of an organic polymer and a polyorganic acid which are at least partially compatible with the inorganic compound to form a polymer blended composition of matter which may be utilized as a membrane in a gas separation process. In addition, it was totally unexpected that a thin film membrane could be cast from such blends to provide a membrane which would be highly selective to certain gases and possess a relatively high ionic conductivity, therefore enabling the membrane to be utilized in such separations involving gases such as hydrogen.
In this respect, U.S. Pat. No. 4,500,667 discloses a polymer blend membrane which may be used for gas separation. However, the membrane which is disclosed in this patent is a binary system as compared to the ternary membrane system of the present invention. The binary system which is disclosed by this patent is a membrane comprising a blend of a heteropoly acid or a salt thereof in an amount of from about 10% to about 70% by weight with from about 90% to about 30% by weight of a polymer which is compatible with these acids or salts such as poly(vinyl alcohol), poly(vinyl fluoride), polyethylene oxide, polyethyleneimine, etc. However, it has now been discovered that the ternary membrane system of the present invention will provide membranes which possess resistivities which are much less than the organic-inorganic polymer blends previously found.